sulfur isotope fractionation during the reduction of...
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Geophysical Research Abstracts,Vol. 11, EGU2009-2604-1, 2009EGU General Assembly 2009© Author(s) 2009
Sulfur isotope fractionation during the reduction of elemental sulfur andthiosulfate by Dethiosulfovibrio spp.A.V. Surkov (1), M.E. Böttcher (1,2), J. Kuever (1,3)(1) Max Planck Institute for Marine Microbiology, Celsiusstr.1, D-28359 Bremen, Germany, (2) present address: LeibnizInstitute for Baltic Sea Research (IOW), Marine Geochemistry, Seestr.15, D-18119 Warnemünde, Germany([email protected]), (3) present address: Materialprüfanstalt (MPA), Bremen, Germany([email protected])
Thiosulfate and elemental sulfur are typical by-products of the oxidation of dissolved sulfide and important sulfurintermediates in the biogeochemical sulfur cycle of natural sediments where they can be further transformedby microbial or chemical oxidation, reduction, or disproportionation. Due to the often superimposing reactionpathways of the sulfur intermediates in natural environments specific tracers are needed to better resolve thecomplex microbial and biogeochemical reactions. An important fingerprint for sulfur cycling is provided bythe microbial fractionation of the stable sulfur isotopes S-34 and S-32. Proper interpretation of isotope signalsin nature, however, is only possible by the calibration with results obtained with pure cultures under definedexperimental conditions. In addition, sulfur isotope discrimination may provide informations about specificencymatic biochemical pathways within the bacterial cells.
In this study, we report the results for the discrimination of stable sulfur isotopes S-32 and S-34 during re-duction of thiosulfate and elemental sulfur by non-sulfate, but sulfur- and thiosulfate-reducing bacteria which arephylogenetically not related to sulfate-reducing bacteria. Experiments with were conducted at known cell-specificthiosulfate reduction rates. Stable sulfur isotope fractionation was investigated during reduction of thiosulfateand elemental sulfur at 28°C by growing batch cultures of Dethiosulfovibrio marinus WS100 (type strain DSM12537) and Dethiosulfovibrio russensis (type strain DSM 12538) using citrate as carbon and energy source. Thecell-specific reduction rates were 0.3 to 2.4 fmol cell-1 d-1 (thiosulfate) and 31 to 38 fmol cell-1 d-1 (elementalsulphur), respectively. The sulfide produced was depleted in S-34 by 12 per mil compared to total thiosulfate sulfur,close to previous results observed for sulfate-reducing bacteria, indicating that the thiosulfate-reducing mechanismof sulfate reducers is similar to that of the investigated thiosulfate-reducing strains. Elemental sulfur reductionyields sulfide depleted in S-34 and isotope fractionation effects between 1.3 and 5.2 per mil for Dethiosulfovibriorussensis and 1.7 and 5.1 per mil Dethiosulfovibrio marinus, with the smaller fractionation effects observed in theexponential growth phase and enhanced discrimination under conditions of citrate depletion and cell lysis.